Traditional devices for architectural lighting (e.g., indoor residential lighting, commercial lighting, theatrical stage lighting, etc.) use hot tungsten filaments as the light-emitting source. Such devices are commonly being replaced with ones that use newer technology, in which the hot tungsten filament is replaced by a light emitter which is more energy-efficient, or offers more flexibility in features and performance, or both. One such technology gaining rapid adoption is LED (Light-Emitting Diode) lighting. While offering advantages over tungsten lighting as a light source for human vision, LED lights pose significant challenges for digital image capture, both in still photography and in videography. Among these challenges is the variation in light intensity with LED-based lighting.
A common technique for dimming LED lights is the use of pulse-width modulation (PWM.) When PWM is used to dim an LED light, its effect is to cause the LED to cycle between full light output and zero light output. This cycling between “full on” and “full off” is done at a frequency high enough to be invisible to the human eye, and is perceived by humans as a reduction in light intensity where the light appears to be dimmed. However, such cycling can be captured by modern digital imaging systems that use a shutter to define specific exposure periods with the exposure periods typically being a small fraction of a second. For example, when an LED light is dimmed using PWM such that it is cycling between “full on” and “full off” 100 times per second: 5 ms on, then 5 ms off, then 5 ms on, etc. If a digital camera is used to capture a photo using a shutter speed of 1/1000 s (1 ms), then depending on the exact time the shutter is tripped, the exposure might be made during a period when the LED is on, or a period when the LED is off. These two cases would result in very different exposures. This phenomenon imposes limits on shutter speed which can be used when doing still photography or videography under LED lighting. Depending on the specific circumstances, such limitations can be inconvenient, or they can be insurmountable obstacles to good image capture. Example: if one is photographing sports, a relatively high shutter speed (e.g., 1/1000 s) is required to “freeze” subject motion. If the above-described phenomenon imposes a relatively low limit on the shutter speed which can be used (e.g., 1/100 s), then producing high-quality action photographs will be impossible.